Most present-day cellular networks offer circuit switched services for speech and data. The available frequency band is divided between these services, all having equal priority. The network does not take into account whether the capacity is used for the transmission of speech or data.
Considering burst-form data services, circuit switching does not exploit the channel optimally. Therefore packet radio services are used alongside existing circuit switched services in cellular networks. Since the existing radio band cannot be expanded, packet radio services must be fitted into the same band as circuit switched services. Thus a certain amount of capacity has to be taken from circuit switched services for packet radio services.
In TDMA cellular systems, a radio band is usually divided into multiple frequency bands (FDMA, Frequency Division Multiple Access), and each frequency band is further divided into multiple time slots. Logical channels are transmitted in the physical time slots of the radio interface. In circuit switched cellular systems, all time slots are used for control signaling and for circuit switched traffic.
Cases associated with this topic have been discussed previously in certain patent publications. One example of them is EP-26 11 27, which describes a time-sharing telecommunications system wherein the spectrum is exploited in a relatively efficient manner by dividing narrow-band radio frequency channels into at least two time slots, one to transmit coded speech signals and one to provide two-way transmission. However, this publication does not discuss the dynamic allocation of capacity, and it does not discuss packet radio services as such.
U.S. Pat. No. 4,887,265 discloses a packet radio switched cellular system. In this system, a plurality of data calls can be switched to one and the same radio channel, whereby radio spectrum is saved. However, the publication mainly discusses the criteria of handoff. It does not discuss the dynamic allocation of capacity to packet radio and circuit switched services.